Pulsed operation of high-power light emitting diodes for imaging flow velocimetry

Willert, Christian; Stasicki, Boleslaw; Klinner, Joachim; Moessner, Steffen

doi:10.1088/0957-0233/21/7/075402

Cited by 154 publications

(122 citation statements)

References 15 publications

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“…Although light-emitting diodes can be used as the light source for PIV measurements, which was shown by Willert et al in 2010 [114], shorter pulses with higher energy are achievable with pulsed lasers. This is in particular crucial for high-speed PIV measurements.…”

Section: Space Measurementmentioning

confidence: 99%

Imaging Flow Velocimetry with Laser Mie Scattering

Fischer

2017

Applied Sciences

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Abstract:Imaging flow velocity measurements are essential for the investigation of unsteady complex flow phenomena, e.g., in turbomachines, injectors and combustors. The direct optical measurement on fluid molecules is possible with laser Rayleigh scattering and the Doppler effect. However, the small scattering cross-section results in a low signal to noise ratio, which hinders time-resolved measurements of the flow field. For this reason, the signal to noise ratio is increased by using laser Mie scattering on micrometer-sized particles that follow the flow with negligible slip. Finally, the ongoing development of powerful lasers and fast, sensitive cameras has boosted the performance of several imaging methods for flow velocimetry. The article describes the different flow measurement principles, as well as the fundamental physical measurement limits. Furthermore, the evolution to an imaging technique is outlined for each measurement principle by reviewing recent advances and applications. As a result, the progress, the challenges and the perspectives for high-speed imaging flow velocimetry are considered.

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Section: Space Measurementmentioning

confidence: 99%

Imaging Flow Velocimetry with Laser Mie Scattering

Fischer

2017

Applied Sciences

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“…A pulsed, overdriven current LED system based upon the work in [33][34][35][36][37][38] was developed for use in this study. The system consisted of a high power, green Phatlight CBT-40 LED [39] which is rated to operate with a current of 5.9 A continuous or 9.8 A pulsed (50% duty cycle).…”

Section: Led Illumination Systemmentioning

confidence: 99%

“…In the work [37] this same LED was shown to increase in light emission with increasing drive current with a proportionality of approximately 0.35 beyond currents of 10 A. Using the 0.35 proportionality, the increase in current from 9.8 A to the 60 A used in this study will result in an effective pulse power of 21 W. Fine tuning of camera and LED syncing was possible by inducing a small delay in the camera from the trigger to account for any discrepancies between the LabView clock and the camera clock and any lag induced in the system.…”

Section: Led Illumination Systemmentioning

confidence: 99%

Optical characterization of Diesel and water emulsion fuel injection sprays using shadowgraphy

Emberson

Ihracska

Imran

et al. 2016

Fuel

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h i g h l i g h t sFuel injection sprays have been examined using a focused shadowgraph system. Diesel and Diesel and water emulsions containing 10% and 20% water examined. Temporal evolution of the spray cone angle and tip penetration have been measured. Emulsification reduced the cone angle at injection pressure of 500 bar. Emulsification had no discernable influence on the tip penetration. t r a c tDiesel fuel and water emulsions have been shown to reduce emissions of NO x and PM from compression ignition engines. There is a lack of work examining the influence of emulsification on the sprays formed during injection. This work examines the spray cone angle and tip penetration of Diesel fuel and water emulsions, containing 10% and 20% water (by mass). All experiments were conducted under nonreacting, non-vaporizing conditions in a constant volume pressure chamber filled with nitrogen. A focused shadowgraph system, with high speed photography, coupled with a research, high current LED system was used. Differences in the spray cone angle suggest the emulsification did have an effect for the injections at a pressure of 500 bar. Emulsification had no discernible effect on the spray tip penetration. Spray tip penetration showed agreement with previous trends in terms of proportionality to time after start of injection however agreement with models found in the literature was not consistent.

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“…Currently, there is a trend towards, designing cost effective PIV systems. Light Emitting Diodes (LED) have number of attractive features like low cost, low power consumption and high brightness which are necessary for PIV experiments (Willert et al (2010) [14], Buchmann et al (2012) [15]). The literature reports the use of LEDs for bubble shadowgraphs [16,17] shadow velocimetry [18] and for PIV [14].…”

Section: Introductionmentioning

confidence: 99%

“…This system has the capability of measuring 10 µm particles with 1 ms −1 in water and 50 µm droplets with 10 ms −1 in air. Willert et al (2010) [14] investigated high power pulsed operation LEDs for measuring flow characteristics using side scattering technique.…”

Section: Introductionmentioning

confidence: 99%

Particle Image Velocimetry with high power Light Emitting Diodes for flow through porous medium

Harshani

Galindo‐Torres

Scheuermann

2015

Computational Methods in Multiphase Flow VIII

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Particle Image Velocimetry (PIV) is a non-invasive optical measurement technique which has been used for many decades to measure fluid velocity. Conventionally, PIV systems are equipped with a laser system for illuminating the flow field. However, laser systems are expensive, and their usage usually creates specific safety precautions. In this work, we used a low cost LED based illumination system in conjunction with the refractive-index matching method to measure flow velocities in porous media. Hydro jelly beads were used as a transparent porous medium which have the same refractive index as water. The movement of tracer particles which were illuminated by the LED pulse was captured by a high-speed double pulsed camera and the resulting images were processed for receiving the pore-scale fluid velocity. Interstitial velocity vectors averaged over a specified region were presented and compared with the vertical velocity component calculated from the volumetric flow rate. In general, our results demonstrated the usability of LED based PIV system for investigating flow conditions in porous media. The future aim of this study is the investigation of micro-scale seepage induced internal erosion of granular structures.

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Pulsed operation of high-power light emitting diodes for imaging flow velocimetry

Cited by 154 publications

References 15 publications

Imaging Flow Velocimetry with Laser Mie Scattering

Imaging Flow Velocimetry with Laser Mie Scattering

Optical characterization of Diesel and water emulsion fuel injection sprays using shadowgraphy

Particle Image Velocimetry with high power Light Emitting Diodes for flow through porous medium

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